It will be really helpful if someone can help me understand this and similar other phrases used in the XPS explanation.
Well, 4f is an electron from a 4f electron, but I guess you knew that part, already, right?
The indices 7/2 and 5/2 indicate that the electrons exhibit coupled states thus resulting in a split signal. For any angular momentum or spin phenomenon multiplicities of coupled states are calculated by 2J+1, that means you should observe two 4f signals whose intensities should have the ratios:
7/2*2+1=8
5/2*2+1=6
->8/6=4/3=I(4f7/2)/I(4f(5/2)
In reality you will observe slight deviations from that because the cross sections for the photoemission are not fully identical. Therefore, if you evaluate your XPS in order to calculate a stoichiometry, check out whether your software is using a set of cross sections that includes coupling or one that doesn't.
The most popular sets are probably the Scofield and the Yeh sets; Scofield includes this effect while Yeh doesn't; on the other hand, Yeh used a slightly better calculation method, so for the choice of the set I would set the preference like this:
-you don't use peaks with coupled signals (as in most of my own XPS work) -> Yeh
-your evaluation requires the interpretation of coupled signals ->Scofield
Dear Farooq Adil Syed,
This is due to spin-orbit splitting.
First we must remember the quantum numbers:
n: main quantum number
l: angular momentum quantum number
ml: magnetic quantum number
s: spin quantum number
At this point we will focus on l and s.
l = 0, 1, 2, 3 (s, p, d, f)
s = 1/2, -1/2.
And finally we have j: total angular momentum.
j = l ± s.
So for example in your case a 4f orbital
l = 3, then j = 3 + 1/2 and j = 3 - 1/2
j = 7/2 and j = 5/2.
Orbital l j Area ratio (2j + 1)
s 0 1/2 -
p 1 3/2, 1/2 4:2 (2:1)
d 2 5/2, 3/2 6:4 (3:2)
f 3 7/2, 5/2 8:6 (4:3)
Just saying that one is spin up and one down is wrongly overfacilitating; those coupled states are degenerate and each involves a number of energetically equivalent states (that's where the multiplicity comes from). You will only be able to differentiate between "up" and "down" cases if you apply a Zeeman or Stark effect scenario which is not the case in usual XPS.
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